Device for detecting a gas having an excitation device for exciting the gas by an electromagnetic wave having a wavelength corresponding approximately to that of the gas; and a detection device for detecting the excitation of the gas, the detection device having a waveguide connected to the excitation device, a part of which forms a movable element designed to be in contact with the gas and capable of being set into vibration by the impact of the excited gas molecules; and a measurement sensor, for measuring the vibration of the element, the measurement sensor and the element forming the detection device.